SQLAlchemy ORM - 应用过滤器

在本章中，我们将讨论如何应用过滤器以及某些过滤操作及其代码。

可以使用 filter() 方法对 Query 对象表示的结果集进行某些条件约束。过滤方法的一般用法如下 −

session.query(class).filter(criteria)

在下面的例子中，对 Customers 表执行 SELECT 查询得到的结果集通过条件 (ID>2) 进行过滤 −

result = session.query(Customers).filter(Customers.id>2)

该语句将转换为以下 SQL 表达式 −

SELECT customers.id
AS customers_id, customers.name
AS customers_name, customers.address
AS customers_address, customers.email
AS customers_email
FROM customers
WHERE customers.id > ?

由于绑定参数（？）为 2，因此只会显示 ID 为 column>2 的行。完整代码如下 −

from sqlalchemy import Column, Integer, String
from sqlalchemy import create_engine
engine = create_engine('sqlite:///sales.db', echo = True)
from sqlalchemy.ext.declarative import declarative_base
Base = declarative_base()

class Customers(Base):
   __tablename__ = 'customers'
   
   id = Column(Integer, primary_key = True)
   name = Column(String)

   address = Column(String)
   email = Column(String)

from sqlalchemy.orm import sessionmaker
Session = sessionmaker(bind = engine)
session = Session()
result = session.query(Customers).filter(Customers.id>2)

for row in result:
   print ("ID:", row.id, "Name: ",row.name, "Address:",row.address, "Email:",row.email)

Python 控制台中显示的输出如下−

ID: 3 Name: Rajender Nath Address: Sector 40, Gurgaon Email: nath@gmail.com
ID: 4 Name: S.M.Krishna Address: Budhwar Peth, Pune Email: smk@gmail.com